This invention relates to private electronic telephone systems and is concerned primarily with such systems intended for use in installations of intermediate size, that is to say, between ten and one hundred internal extensions.
Small installations comprising of about ten internal telephone extensions are normally catered for by key type systems, which are economical and usually quite adequate for small installations. Large installations, on the other hand, having several hundred or several thousand internal telephones, require complex switching systems and are usually served by PABX systems which, although involving a high capital cost, can be economically justified since the cost is shared over a large number of extensions. However, a problem arises in the case of an installation of intermediate size, having up to about one hundred extensions, in which a key type system would not provide the required flexibility and in which the capital cost of a PABX system would usually be prohibitively high. There is a very large, and increasing, demand for private telephone exchanges in the intermediate size range, wherein considerations of operational flexibility and economy of installation are of critical importance, and the demand has given rise to the need for a new electronic technology which can be so applied. The present invention provides such a technology.
According to one aspect of the present invention there is provided an electronic telephone system having a plurality of terminal units which are connected radially to a central equipment by respective cables each including at least one conductor pair providing a transmission path for system signalling, said conductor pairs being connected to a common control unit at the central equipment, the common control unit including: a timing generator for generating address signals and timing signals, multiplexing means controlled by the timing generator in accordance with the generation of said address signals for placing the units sequentially in communication with the common control unit for exchanging information therewith, said terminal units being scanned in cyclic sequence, each unit being allotted a unique time slot within the scanning cycle, and means responsive to timing signals from the timing generator for controlling the transmission of data over said system signalling paths, said means dividing each of said allotted time slots into distinct periods in which data is transmitted unidirectionally from the terminal unit to the common control unit and in which data is transmitted from the common control unit to the terminal unit, respectively, the conductor pairs being connected to transmit both system signals and d.c. power for consumption at the terminal units and each said conductor pair being a balanced pair terminated by a matching impedance at the respective terminal unit.
According to another aspect of the invention there is provided an electronic telephone system having a plurality of extension line units which are connected radially to a central equipment by respective cables each including a first conductor pair providing a speech transmission path and a second conductor pair providing a separate transmission path for system signalling, said first and second conductor pairs being connected respectively to a crosspoint matrix and to a common control unit at the central equipment, the common control unit including: a timing generator for generating address signals and timing signals, multiplexing means controlled by the timing generator in accordance with the generation of said address signals for placing the extension line units sequentially in communication with the common control unit for exchanging information therewith, the extension line units being scanned in cyclic sequence, each unit being allotted a unique time slot within the scanning cycle, and means responsive to timing signals from the timing generator for controlling the transmission of data over said system signalling paths, said means dividing each of said allotted time slots into distinct periods in which data is transmitted unidirectionally from the extension line unit to the central control unit and in which data is transmitted unidirectionally from the central control unit to the extension line unit, respectively, the conductor pairs being connected to transmit both system signals and d.c. power for consumption at the terminal units and each of said second conductor pairs being a balanced pair terminated by a matching impedance at the respective extension line unit.
Preferably, where the extension line units are associated with respective telephone instruments, each telephone instrument has a control panel including a keypad and a set of indicator lamps operatively associated with respective particular keys thereof, and each extension line unit includes means responsive to key operation for transmitting data to the common control unit in accordance with such operation, and means responsive to data received from the common control unit for selectively controlling the lamps in accordance with line signalling conditions, said lamps when operating indicating the status of connections to respective connected parties, each lamp being operable in different modes according to the status of the respective connection, each of said particular keys being operable to modify the status of the connection indicated by the associated indicator lamp.
According to yet another aspect of the invention there is provided in an electronic telephone system having a plurality of extension line units which are connected radially to a central equipment by respective cables each providing separate paths for speech transmission and system signalling, each said signal transmission path being constituted by a balanced conductor pair terminated at the respective unit by a matching impedance, circuit means for effecting bidirectional signalling along the conductor pair, said circuit means comprising a differential amplifier connected across the matching impedance for receiving data pulses from the central equipment, data processing means connected to receive the amplifier output, an electronic switching device connected across the conductor pair, and means for operating the electronic switching device in accordance with signals to be transmitted to the central equipment for applying data pulses across the pair.
According to yet another aspect of the invention there is provided an electronic telephone system having a plurality of extension line units which are connected radially to a central equipment by respective cables each providing separate paths for speech transmission and system signalling, each of said system signalling paths including a balanced pair adapted for bidirectional transmission of pulse signals, each extension line unit including: a matching impedance terminating the balanced pair, a differential amplifier having input terminals connected across the matching impedance, the amplifier having an output circuit for deriving data pulses in accordance with pulse signals received from the central equipment, a serial-to-parallel converter connected in said amplifier output circuit to control the receipt of data pulses therefrom, a latching circuit for storing the output of the serial-to-parallel converter, indicators responsive to the latched output of the serial-to-parallel converter for indicating a called condition, switching means for initiating data to be transmitted to the central equipment in accordance with the signalling condition of the extension line unit, pulse generating means responsive to said switching means for generating data pulses to be transmitted to the central equipment, and an electronic switching device connected across the balanced pair, said electronic switching device being responsive to the generated pulses for applying voltage pulses across the conductor pair.
According to yet another aspect of the invention there is provided in an electronic telephone system including a solid-state crosspoint matrix operable by a central control for selectively interconnecting calling and called parties in accordance with system signalling conditions, the system serving at least one trunk having tip and ring leads constituting a trunk pair, the system further including a trunk interface connected to the crosspoint matrix by a conductor pair providing a speech transmission path and to the central control by conductors used for system signalling, the trunk interface comprising: a first resistance hybrid network providing a first pair of network terminals connected to said tip and ring leads, and second and third pairs of network terminals, the network providing a matching impedance terminating the trunk pair, a second resistance hybrid network having a first pair of network terminals connected to the conductors of said conductor pair, and second and third pairs of network terminals, the second resistance hybrid network providing a matching impedance terminating said conductor pair, the second pair of network terminals of each resistance hybrid network being connected to the third pair of network terminals of the other network by respective circuits each providing a unidirectional path for speech transmission, said circuits including control means responsive to trunk signalling connected to the central control, said control means including respective switching means responsive to incoming and outgoing call signals for rendering the circuits operable and inoperable in accordance with calling conditions.
According to yet another aspect of the invention there is provided in an electronic telephone system having a plurality of extension line units and an attendant's unit connected to a common control for exchanging data therewith, said units being scanned sequentially by the common control in a time-division-multiplex mode, each unit being allotted a unique time slot within the scanning cycle, the attendant's unit comprising:
a console having a plurality of keys operable for making line connections and effecting line control functions, the console having an associated circuit including switching means actuated by the keys for initiating the transmission of coded data to the central control in accordance with such key operation, said associated circuit including:
a free running clock oscillator furnishing clock pulses,
gating means for gating said clock pulses with timing pulses defining the time slot allotted to the attendant's unit,
a counter having input circuit means connected to receive the output of said gating means, and output circuit means connected to a decoder for decoding the output of the counter, the decoded output providing binary address signals for the keys,
said switching means being sequentially scanned in accordance with the generation of said binary address signals,
latching means for latching the output data of an actuated one of said switching means first detected by such scanning, the output data being stored by the latching means until release of the associated key,
and means for releasing said stored data to the central control.
According to yet another aspect of the invention there is provided a private automatic branch exchange system having a plurality of extension line units associated with respective telephone instruments, said extension line units being connected radially to a crosspoint matrix and to a common control unit by respective conductor pairs providing separate paths for speech transmission and for system signalling, the signalling pairs being balanced pairs each terminated by matching impedances, the system further including a plurality of trunk interface units each providing a speech transmission path connected to the crosspoint matrix and a separate transmission path for system signalling connected to the common control unit, the extension line units and trunk interface units being cyclically scanned by the common control unit in a time-division-multiplex mode, the common control unit including a central processor responsive to respective line signalling conditions for generating control signals and supervisory signals in accordance therewith, and the crosspoint matrix being responsive to said control signals for selectively interconnecting said speech paths for connecting local and trunk calling parties to local and trunk called parties, each said telephone instrument having a keypad and a set of indicator lamps, the associated line unit including a transmitter circuit including switches operable by the keypad for initiating transmission of data to the control unit in accordance with key operation and a receiver circuit including decoder means for decoding data received from the control unit and driver means responsive to the decoded data for selectively controlling the lamps to indicate designated line signalling conditions.
A system according to the invention is preferably capable of providing a full range of PABX facilities, some of which may be available as optional additions to the basic system. The basic system may include facilities for direct outward dialing, directly connected internal calls; group calls; night service arrangements, inward and outward call restriction by class of service fields; call transfer by individual extensions or by attendant; consultation hold and three-way conference calls; power fail transfer; trunk answer from any station; push-button "dialing"; call waiting signal; connections to tie trunks; tandem switching of the tie trunk calls; C.C.S.A. access; call pick-up; two-way call splitting; secrecy; camp-on; and indication of camp-on. Optional additions may include facilities for identified outward dialing; speed calling; access to paging systems and code-call system; Toll denial; recorded telephone dictation; "barge-in", etc.